This invention relates to thermosetting acrylic enamels and, in particular, to an improved thermosetting acrylic enamel that gives a high quality finish that is useful for the exterior of automobile and truck bodies.
Thermosetting acrylic enamels are well known in the art as shown by Frazier et al. U.S. Pat. No. 2,681,897, issued June 22, 1954; Vasta U.S. Pat. No. 3,338,860, issued Aug. 29, 1967; Fisk et al. U.S. Pat. No. 3,365,414, issued Jan. 23, 1968; and Lowe et al. U.S. Pat. No. 3,411,941, issued Nov. 19, 1968 and are excellent for many purposes. However, as is typical of enamel compositions, spot repair of these enamels is difficult and appearance of finishes of these enamels is not of the quality of lacquer finishes.
A thermosetting acrylic enamel shown by Parker U.S. Pat. No. 3,637,546, issued Jan. 25, 1972, provides a finish that is comparable to an acrylic lacquer finish and can be spot repaired. A technique used to repair lacquer finishes can be used to repair a finish of Parker's enamel, i.e., a solvent mist is applied to soften a damaged area of the finish and a repair coating is applied and then baked and an unnoticeable repair is formed.
Finishes of Parker's enamels can be applied to automobile and truck bodies with typical automotive production equipment and have a good appearance, good gloss, and resistance to weathering, water spotting and gasoline. However, one particular problem which the automobile and truck manufacturing industry has found to be unacceptable is that these finishes, particularly finishes containing aluminum flake, when exposed to conditions of high temperature and humidity only for relatively short periods lose gloss rapidly, blister slightly and darken.
U.S. Pat. No. 3,074,895, issued Jan. 22, 1963 to Jackson, shows the use of iron pyrophosphate pigment to improve durability. However, only relatively large amounts of iron pyrophosphate were shown to be effective, in finishes other than thermosetting acrylic enamels.